Aerial radiating with different beamwidth in two perpendicular planes

ABSTRACT

Aerials to provide a very high directivity (1* approx.) in one plane and a much lower directivity in the plane perpendicular are made of a primary source feeding a dielectric lens shaped according to the volume obtained by rotating around an axis a broken curvilinear line which crosses said axis at two distinct points and admits a plane of symmetry perpendicular to said axis and is made of a dielectric material the varying index of which is a function only of the distance to the axis.

AU 255 EX inventors Bernard Chimn;

Loub Dufiau, Paris, France Appl. No. 734,583 Filed June 5, 1968 Patented Apr. 27, 197] Assignee Societe Lignes Telegraphiques Et Telephoniques Park, France AERIAL RADIATING WITH DIFFERENT BEAMWIDTH IN TWO PERPENDICULAR PLANES 5 Claims, 4 Drawing Figs.

US. Cl. 343/753,

343/91 l Int. Cl Hillq 19/06 Field of Search 343/753,

[56] References Cited UNTIED STATES PATENTS 230L412 7/l957 Maybury et a] 343/753 3,015.]02 l2/l96l Crane et al. 343/91 lL 3,108,278 10/1963 Walter 343/753 3,329,958 7/1967 Anderson 343/753 3,255,452 6/ l966 Walter et al. 343/753 Primary Examiner-Herman Karl Saalbach Assistant ExaminerSaxfield Chatmon, .Ir. Anomey-Kemon, Palmer & Estabrook ABSTRACT: Aerials to provide a very high directivity (1 approx.) in one plane and a much lower directivity in the plane perpendicular are made of a primary source feeding a dielectric lens shaped according to the volume obtained by rotating around an axis a broken curvilinear line which crosses said axis at two distinct points and admits a plane of symmetry perpendicular to said axis and is made of a dielectric material the varying index of which is a function only of the distance to PATENTED APR 2 7 I9" sum 2 BF 3 Figz2 M ya PATENTED mzmn SHEET 3 OF 3 3 NF mp 3 m- AERIAL RADIA'I'ING WITH DIFFERENT BEAMWIDTII IN TWO PERPENDICULAR PLANES BACKGROUND OF THE INVENTION The invention is related to the design of an antenna which will provide a diagram a few degrees wide in one plane and a few tens of degrees wide in a plane perpendicular to the first one. It is already known to design antennas with beam widths differing from one plane to another. British Pat. No. 796,549 flled on Aug. 2, 1956 for Aerials" discloses the combination of a primary source with a reflector which meets this requirement. The high complexity reflector which is necessary leads to high manufacturing cost of the antenna specially when the wavelength is short due to the mechanical precision required. The object of the prsent invention lies in a structure which requires very little machining and consists in a primary source linearly polarized illuminating a dielectric lens made through moulding and glueing of plastic material shells. The antennas according to the present invention are les bulky than the rectified reflectors of the prior art'and much lighter. Therefor to their lower manufacturing cost is to be added a substantial decrease of the installation price and a much easier operation. From the operational point of view the antennas according to the present invention show another important improvement over the prior art in the readiness of electronic and mechanical scanning of the beam in the high directivity plane. Another advantage of the antennas according to the invention lies in the gain which is higher than db. in most of the embodiments.

RAPID DISCLOSURE OF THE INVENTION The antennas according to the present invention rely on the v following basis: a linearly polarized source is associated with a lens which is a volume generated by a planar curvilinear-linear broken line rotating around an axis said line having two crossing points with said axis and a plane of symmetry perpendicular to the axis, made of a dielectric the index of which is only function of the distance of the point considered to the axis of the volume. The broken curvilinear-linear line may have any shape such as a mixed linear and curvilinear rectangle with two linear sides perpendicular to the axis and the remaining side as an arc of circle the center of which is located on the axis. In another embodiment the planar broken line is part of an ellipse or of a parabola or the combination of such curves. The refractive index follows a law of variation with respect to the distance from the axis of the volume which is a constant less the square of the ratio of the distance to the axis to the distance between the surface of the lens and said axis along the line which passes through said point. Additional means are also provided to adjust the difference in the path of the rays within the lens.

DETAILED DISCLOSURE In order to fully understand the scope of the invention it is necesary to refer to the theoretical work on propagation published by Prof. R. K. Luneberg and entitled Mathematical Theory of Optics" published by Brown University, Providence, R.l., U.S.A. in l944. This work is the background for designs called Luneberg Lenses which are well known from the men of art. They may be summarized as dielectric lens structures having a complete symmetry, that is spherical solid structures in which the refractive index at any point is given by the formula:

where: x is the distance of the point from the center n is the refractive index R is the radius of the sphere.

When the source is located at any point on the surface of the lens, formula (1) is the condition to get a planar radiated wave. When the source is not on the sphere, another formula can be calculated to meet the condition for a planar radiated wave. From the practical point of view, condition l) is sufficiently approximated when the sphere is made of a series of concentric shells made each one of material of constant index, the indexes of the different shells meeting equation (1) by steps. The index for each shell is chosen through equation l considering x is the mean diameter of the shell. When such a structure is illuminated with a point source located at any point on its surface, the radiated beam consists of parallel rays, that is the equiphase surface is a plane; the angular aperture of the beam at 3 db. is given by:

where A is the wavelength of the radiated wave D is the diameter of the lens (equal to 2R according to the equation l As is well known these lenses are of particular interest when scanning of the beam is required since it can be obtained by any movement of source on the surface without change of the radiated beam characteristics.

From the theoretical point of view, the present invention is based on Lunebergs work. It consists in a linearly polarized source feeding a dielectric lens meeting Lunebergs law (I) which admits a symmetry of revolution only in the plane where high directivity is required and has smaller dimensions than the Luneberg sphere along any direction perpendicular to said plane. From the theoretical point of view, the lens may be considered as a Luneberg sphere from which two portions have been cut off symmetrically with respect to a plane passing by the center of said sphere. By shortening the structure, a widening of the beam is obtained.

FIGS. 1 and 2 show such a structure and its radiation characteristics. The shape of lens I of H6. 1 is a sphere of diameter D and center 0 from which two identical portions 2 and 3 have been removed symmetrically with respect to plane xOy as shown by the dashed lines. The outline of the lens is shown by the heavy line AECB and it is symmetrical with respect to the Oz axis. The dimension of the lens along Oz is h. The lens can be considered as obtained by rotating the linearcurvilinear rectangle AECB around its linear side AB (axis Oz). Linear sides AE and BC describe planes. The arc of circle EC, the center of which is located on AB describes a part of a sphere. The lens is designed as a series of concentric shells of constant refractive index meeting Lunebergs law.

Curve 0, in FIG. 2 shows the measured values of the angular aperture in plane xOy versus the ratio D/h when the linear polarization of the source is parallel to 0x. 6, is practically independent from the parameter D/h. The curve labeled 0, represents the variations of the angular aperture of the beam radiated in a plane perpendicular to xOy. It appears that this aperture is very sensitive to the values of parameter D/h. The values for 6, match the values calculated by the Luneberg theory for a spherical lens. In the case of the structure shown in FIG. 1 the aperture of the beam in a plane perpendicular to xOy approximates the following law:

A is the wavelength D is the diameter of the lens I: is the height along axis Oz.

The curves of FIG. 2 refer to a 10-inch diameter lens fed with a rectangular waveguide axes of which are directed along the Ox and the Oz directions and the wave propagates along 0y at a frequency in the 9 GHz. range.

The level of the secondary lobes of such an antenna depends on the illumination law from the source. With a given source, the level and the gain vary when the orientation of the polarization plane is varied with respect to the xOy plane. For instance, for the value and the large side of the rectangular waveguide directed along Oz. the maximum secondary lobe is at db. of the main lobe in the E plane and at l5 db. in the H plane. When the small dimension of the waveguide is along Oz, the level of .the secondary lobe is l 5 db. in the E plane and l0 db. in the H plane. The above values of the secondary lobes attenuation may be too small for some applications. The embodiments shown in FIGS. 3 and 4 provide a higher attenuation of the secondary lobe as will be explained later. The gain is 21 db. when the small side of the waveguide is along Ox and i8 db. when this side is along the Oz direction. The variations of the gain according to parameter D/h are shown in table 1 where E refers to the electric field in the cross section of the guide acting as a source.

TABLE 1.GAINS Any diagram may be obtained starting from a spherical Luneberg lens and removing two identical portions of the sphere. Of course, this way of operating is just for experimentation sake. so as to provide the designer with the curves of FIG. 2. When families of curves such as shown in FlG. 2 are available, the designer is able to select the proper values of h and D which will meet his particular requirement. The lenses are then manufactured by moulding the shells as is well know per se.

As already mentioned, the level of the secondary lobe and the gain value may not meet the operating requirements. The rather high secondary lobe level lies in the difference of path length between the difierent rays within the lens. Such a ray is shown as SP in FIG. 1. When the exit point P is displaced along the surface across the successive shells, the index at the exit point changes by step. Since the index of the intermediate shells is different from that of the air, a partial reflexion occurs. This explains the loss of gain and the lower secondary lobe attenuation. This drawback may be minimized by properly designing the shape of the external surface of the lens, and/or providing phase correcting means along the non spherical parts of the surface as shown respectively in FIGS. 3 and 4.

FIG. 3 shows the cross section of a lens in which the external surface is selected in view of better phase match of the radiated rays, by plane 0: containing the propagation direction Oy. Curves A'E' and B'C are arcs of parabolas. The volume of the lens can be considered as obtained by rotating AB'C' around A'B. Calculation made considering the index values of the successive shells according to Luneberg's law, show that the path of the rays inside the lens is nearer to integral values of wavelength than in the structure shown in FIG. 1.

The embodiment shown in F IG. 4 is the structure of FIG. 1 with phase matching means added in view of compensating the reflection at the surface. l, ll, lll, lV show the different shells composing the lens which intersect the planar faces AE and BC. Each shell is terminated by a dielectric lamination 11, 12, l3...1l, 12'... made ofthe same material as the associated shell. The direction of each of said larninations is parallel to the mean ray issuing from said shell as shown at SP,, SP SP The length of each lamination along the direction of the mean ray is calculated so that the path of the corresponding ray is a multiple of the wavelength. in the plane perpendicular to the FIGURE, the lamination is a trapeze. The thickness of the lamination does not vary along the Ox axis.

We claim: I I l. A dielectric lens-type antenna with high directivlty in one plane and poor directivity in a plane perpendicular thereto and in which the index of refraction of the dielectric follows Luneberg's law, said lens comprising a three dimensional solid which is symmetrical with respect to an axis lying in the plane of poor directivity, said lens having a height h measured along said axis of symmetry and a diameter D in a plane perpendicular to said axis such that 6 equals the angular aperture in the plane of poor directivity and k is a constant dependent upon the material used for the lens.

2. An antenna according to claim 1 in which k=0.8.

3. An antenna according to claim 1 in which the lens is a sphere from which two identical portions have been cut perpendicularly to said axis of symmetry.

4. An antenna according to claim 1 in which the configuration of the lens is defined as a solid obtained by rotating around an axis a curvilinear-linear broken line cutting said axis at two points spaced from each other by a distance equal to h.

5. An antenna according to claim 1 in which said lens is made of concentric shells of indexes of refraction selected to follow approximately Luneberg's law in which the external faces of each shell are connected to larninations made of the same material as the associated shell designed so as to contain all the rays passing through said external faces so that the radiated wave be planar. 

1. A dielectric lens-type antenna with high directivity in one plane and poor directivity in a plane perpendicular thereto and in which the index of refraction of the dielectric follows Luneberg''s law, said lens comprising a three dimensional solid which is symmetrical with respect to an axis lying in the plane of poor directivity, said lens having a height h measured along said axis of symmetry and a diameter D in a plane perpendicular to said axis such that where theta equals the angular aperture in the plane of poor directivity and k is a constant dependent upon the material used for the lens.
 2. An antenna according to claim 1 in which k 0.8.
 3. An antenna according to claim 1 in which the lens is a sphere from which two identical portions have been cut perpendicularly to said axis of symmetry.
 4. An antenna according to claim 1 in which the configuration of the lens is defined as a solid obtained by rotating around an axis a curvilinear-linear broken line cutting said axis at two points spaced from each other by a distance equal to h.
 5. An antenna according to claim 1 in which said lens is made of concentric shells of indexes of refraction selected to follow approximately Luneberg''s law in which the external faces of each shell are connected to laminations made of the same material as the associated shell designed so as to contain all the rays passing through said external faces so that the radiated wave be planar. 